Oyster drills are common on rocky shores and oyster (Crassostrea gigas) farming areas in Taiwan. Most studies on the oyster drill (Thais clavigera) were on its impact on the oyster industry. However, there are at least three Thais species in the west coast of Taiwan. And the basic biology of T. rufotincta and T. keluo was insufficient. Thus, the present study was undertaken to investigate population biology of the three congeneric drills(Thais spp.), including feeding rate, reproductive characters and population dynamics.
T. clavigera was distributed from Tamsui to Tongkong along the west coast of Taiwan. But, it was rare at Tongkong. T. keluo was primarily found at Tamsui and Tongkong. The distribution of T. rufotincta was from Tongkong to Tamsui and mostly occurred between Tongkong and Taishi.
Mean feeding rates (¡ÓSE) of T. clavigera, T. keluo and T. rufotincta were 0.054(¡Ó0.010), 0.038(¡Ó0.004) and 0.010(¡Ó0.003) oysters/snail¡Eday, respectively. The feeding rate of T. rufotincta was significantly lower than other species (P<0.05). It is suggested that the major damage on oyster culture is caused by T. clavigera and T. keluo.
The spawning seasons of T. clavigera, T. keluo and T. rufotincta were from November to May, from February to September, and from April to October, respectively. The number of eggs per capsule was correlated with the length of the capsule (P<0.001) in T. clavigera, T. keluo and T. rufotincta and the number of eggs (¡Ó 95% C.I.) among them was 203(¡Ó14), 168(¡Ó15) and 43(¡Ó3) per capsule, respectively. The mean egg diameter (¡Ó 95% C.I.) of the three drills was 185(¡Ó3), 175(¡Ó4) and 240(¡Ó6) £gm, respectively.
Positive curve relationships between size and weight were found among Thais spp. (P<0.001). Using the length-frequency data, analyzed by the ELEFAN (Electronic Length Frequency Analysis) program, the seasonalized von Bertalanffy growth parameters for Thais spp. were estimated. The growth performance index (ø') and growth parameter (K) showed a similar trend, i.e. Chiku>Tamsui>Shiangsan for T. clavigera, Tamsui > Tongkong for T. keluo, and Chiku > Tongkong for T. rufotincta. It is suggested that water temperature and food abundance are important factors affecting drills¡¦ growth in the west coast of Taiwan.
The recruitment of T. rufotincta at Chiku and Tongkong had two peaks. It was different from T. clavigera and T. keluo with only one peak. Futher studies are necessary to elucidate the relationship between recruitment with different peak periods among sites and environment variables such as primary production, salinity, current and so on.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0906102-154747 |
| Date | 06 September 2002 |
| Creators | Liu, Yu-Chih |
| Contributors | Hsueh-Wen Chang, Sun-Chio Fong, Chih-Yuan Chen, Li-Lian Liu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0906102-154747 |
| Rights | unrestricted, Copyright information available at source archive |
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